In the art of manufacturing medicament aerosol inhalation devices, recent attention has been aimed at detecting and rejecting potential and actual nonconforming devices. For example, a small percentage of aerosol inhalation devices leak or will leak due to manufacturing defects, such as broken or torn gaskets, loss of proper sealing, defective valve, swollen gasket(s), etc. Such defects cause a loss of aerosol propellant, which adversely affects or otherwise alters the performance of the inhalation device.
Recently, the Food and Drug Administration (“FDA”) has become very concerned with leaking (or otherwise nonconforming or defective) aerosol inhalation devices, particularly MDI's. The performance of an MDI can be significantly altered when the propellant leaks, particularly where the propellant leaks in significantly amounts or at a significant rate. For example, a “gross leaker” may not deliver the medicament at all to the patient. MDI's that leak at more than an insignificant rate may under deliver the medicament. In other words, the medicament delivery from a leaking MDI does not conform to the dosing regimen set forth and approved by the FDA. In that case, the patient may not even realize that the insufficient medicament is being delivered to the lungs.
As a result, the FDA has begun requiring manufacturers to stress test aerosol inhalation devices and subsequently weigh the stressed devices to detect actual and potential nonconforming devices. Leaking MDI's will weigh less than what they are supposed to weigh. Stressed MDI's that lose a predetermined amount of propellant are rejected as nonconforming. The FDA has set conforming standards. The FDA has also set a temperature standard of 55° C.±5° C. for heat stress testing the MDI's.
Many methods and apparatus are available for heating MDI's. The present invention involves using electromagnetic induction heating to heat the electro-conductive materials present in the MDI, such as primarily the aluminum canister. Electromagnetic induction is a method of henerating heat within a metal part. Any electrical conductor can be heated by electromagnetic induction. As alternating current from the generator flows through the inductor, or work coil, a highly concentrated, rapidly alternating magnetic field is established within the coil. The magnetic field thus induces an electric potential in the part to be heated. The part represents a closed circuit. The induced voltage causes current to flow within the part. Eddy currents are typically established. The resistance of the part to the flow of the induced current causes heating.
The pattern of heating obtained by induction is determined by a number of factors: the shape of the induction coil producing the magnetic field, the number of turns in the coil, the operating frequency, the alternating current power input, and the nature of the work pieces. The rate of heating obtained by the coils depends on the strength of the magnetic field to which the part is exposed. In the work piece, this becomes a function of the induced currents and the resistance to electrical flow.
The depth of current penetration depends upon work piece permeability, resistivity, and the alternating current frequency. Since the first two factors vary comparatively little, the greatest variable is frequency. Depth of current penetration decreases as frequency increases. High frequency current is generally used when shallow heating is desired. Intermediate and low frequencies are used in applications requiring deeper heating.
The induction coil and associated components and the processes thereof of the present invention are advantageous. The present invention advantageously heats and stress tests MDI's in a relatively short period of time (i.e., dwell time), which permits in-line processing at high throughput. The present invention also advantageously employs a few relatively simple processing and material handling equipment resulting in low investment, reduced maintenance, high efficiency, and reliability. The present invention is further advantageous in that only the electroconductive portions of the MDI are heated significantly reducing the heating of plastic components (e.g., gaskets and valve components) that are susceptible to being unnecessarily damaged by heat. Still further, the present invention advantageously heat stress tests the MDI's without exposing the MDI's to steam or moisture (except any negligible moisture associated with the sealed heat exchangers) which can ingress into the MDI reducing product performance. Further benefits and advantages of the present invention are set forth herein.